Fat parcelization is the reduction in size of the fat bolus that is produced during fat harvest with a cannula. Several factors control the fat parcel sizing during the harvest of the fat. The greatest influence on the size of the fat parcel is the hole diameter of the cannula. Other factors include the vacuum power used to suck the fat through the hole, and the length of the surgeon's “stroke” during harvest.
Parcelization is needed when transplanting fat during autologous fat transfer/grafting. Presently, the cannulas that are used to parcelize the harvested fat are typically 3 and 4 mm outside diameter cannulas with various hole patterns. These commonly used cannulas will produce fat parcels that are less than 10 mm in diameter. This is because the fat parcels are very compressible and flexible, and relatively large parcels can squeeze through small channels. However, these relatively large fat parcels can plug reinjection needles and equipment. In addition, 10 mm fat parcels are now thought to be too large to ensure that the fat parcel survives reinjection. In particular, it is believed that parcels of this size are too large for nutrients to pass to the interior of the parcel. Recent studies indicate that fat parcels with a diameter of less than 3 mm (for example, about 1 mm) are preferred. In particular, this size should be favorable for ensuring growth in the new location, while avoiding clogging of the tissue transfer hardware.
The size of the fat parcels can be decreased by decreasing the size of the holes in the harvest cannula. However, this slows the harvest procedure unacceptably. Other techniques reduce the size of fat parcels by pulverizing them. However, this can destroy the fat parcels, with the result that they will not revascularize when placed in their new location.